Support for Vector Grid

[mumeraltaf]

Addressing #937 and #563. Added a function to add vector tiles as base layer (namely protobuf) to a map.
Using VectorGrid plugin.
Usage Example: examples/VectorGrid.ipynb

[stickler-ci]

E231 missing whitespace after ','

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E231 missing whitespace after ','

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E231 missing whitespace after ','

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E231 missing whitespace after ','

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W391 blank line at end of file

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F401 'jinja2.Environment' imported but unused
F401 'jinja2.PackageLoader' imported but unused

[ocefpaf]

@mumeraltaf sorry for the long time to review this. Nice stuff and great feature you have here but have you considered creating an external plugin and depend on folium instead?

The reason I say this is b/c we won't be able to maintain the code. I would also recommend you pinning the folium version to ensure the plugin won't break with new updates. (Something you cannot do if this is part if the main folium.)

[Conengmo]

I think this PR is nicely done, code looks good. Thanks for your effort @mumeraltaf! I'm inclined to include this in the repository because:

• It's not that heavy in code
• The underlying library is in the Leaflet github organization
• and seems to be actively maintained

I would propose to move it to it's own plugin module though, since the appeal is not that broad (I assume) and technically it is a plugin.

Furthermore, I think it's best not to include the VectorGridChoropleth since it seems fragile. We've learned from our current Choropleth class that users get confused about how to use it, and much validation and documentation is needed. Let's not repeat a second time.

Also, the two methods in Map should be removed.

Here are links to the two notebooks, which aren't working it seems by the way:
http://nbviewer.jupyter.org/github/AURIN/folium/blob/master/examples/VectorGrid.ipynb
http://nbviewer.jupyter.org/github/AURIN/folium/blob/master/examples/VectorChoropleth.ipynb

[RenoFilla]

OK, so has this functionality been picked up anywhere yet? I like to display airspace using OpenAIP (https://maps.openaip.net) which is a vector tile layer as far as I can see:

var OpenAIP = L.tileLayer('http://{s}.tile.maps.openaip.net/geowebcache/service/tms/1.0.0/openaip_basemap@EPSG%3A900913@png/{z}/{x}/{y}.{ext}', {
attribution: 'openAIP Data (CC-BY-NC-SA)',
ext: 'png',
minZoom: 4,
maxZoom: 14,
tms: true,
detectRetina: true,
subdomains: '12'
});

[Conengmo]

This PR is very stale, so I'm going to close it now. This feature is still welcome, so if somebody wants to pick up the work here and address the comments (#943 (comment)) in a new PR that would be appreciated!

[Conengmo]

This was also partially implemented in #1576, available in the 0.13.0 release.